Computing devices, such as notebook computers, personal digital assistants (PDAs), kiosks, and mobile handsets, have user interface devices, which are also known as human interface devices (HID). Capacitance sensing has been implemented in a wide variety of user interfaces of electronic devices to replace mechanical buttons and other controls in the electronic devices. Examples of capacitance sensing devices include touchpads on notebook computers, touchscreens, and slider controls used for menu navigation in cellular phones, personal music players, and other hand held electronic devices.
Capacitance sensing has many advantages over conventional cursor control devices, mechanical switches, and rotary encoders. A principal such advantage is the lack of moving parts, which allows capacitance sensing to provide great improvements in reliability, since there are no moving parts to wear out.
One type of conventional capacitance sensing device is a slider that operates by way of capacitance sensing utilizing capacitive sensors. The capacitance detected by a capacitive sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In an electronic device, a change in capacitance detected by each sensor in the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. The touch-sensor devices may include single sensor elements or elements arranged in multiple dimensions for detecting a presence of the conductive object on the touch-sensor device. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device, which in turn produces electrical or optical signals representative of the position of the conductive object in relation to the capacitance sensing device, such as in relation to the touch-sensor pad in the X and Y dimensions.
FIG. 1A illustrates a conventional linear touch-sensor slider. The linear touch-sensor slider 110 includes a surface area 111 on which a conductive object may be sensed to control a setting on a device, such as volume or brightness. Alternatively, the linear touch-sensor slider 110 may be used for scrolling functions. The construction of touch-sensor slider 110 may be similar to that of a touch-sensor pad. Touch-sensor slider 110 may include a sensor array capable of detection in only one dimension (referred to herein as one-dimensional sensor array). The slider structure may include one or more sensor elements that may be conductive traces. By positioning or manipulating a conductive object in contact or in proximity to a particular portion of the slider structure, the capacitance between each conductive trace and ground varies and can be detected. The capacitance variation may be sensed as a signal on the conductive trace by a processing device. It should also be noted that the sensing may be performed in a differential fashion, obviating the need for a ground, virtual ground, or other reference. For example, by detecting the relative capacitance of each sensor element, the position and/or motion (if any) of the external conductive object can be determined. It can be determined which sensor element has detected the presence of the conductive object, and it can also be determined the motion and/or the position of the conductive object over multiple sensor elements.
Radial sensing is conventionally done using a radial slider that is used in detecting position information on planar sensor elements disposed in a circular manner, as illustrated in FIG. 1B. The radial sensor array 120 of FIG. 1B includes multiple sensor elements 121 disposed in a circular pattern. Radial sensing may also be done using a touchpad with radius and degree output from the touchpad. Radial sensing using a touchpad, however, uses more complex position algorithms, such as to perform conversion from X and Y locations to a radius and angle. Also, touchpads may have small sensor activation areas, resulting in a decrease in sensitivity.
One type of human interface device that has replaced the mechanical knob with a planar radial slider is small, handheld devices. While a planar radial slider may be appropriate for a small, handheld device, it may not be appropriate for larger appliances, like a wide variety of household appliances, sometimes referred to as white goods, for example, air conditioner, dishwasher, washing machine, clothes dryer, freezer, refrigerator, stove (also referred to as range, cooker, oven, oven range, cooking plate, or cooktop), water heater, toaster oven, blender, heater, mixer, or the like, whose normal user interface includes one or more mechanical knobs. Also, the planar radial slider may not be appropriate for industrial appliances whose normal interface is one or more large mechanical knobs. The traditional implementation of controls on these larger appliances is in the form of mechanical knobs coupled to electromechanical timers, switches, rheostats, and other controls. These knobs are designed to be operated by rotating these mechanical knobs with a complete hand, instead of just a finger as done in a planar radial slider of a handheld device.
Mechanical knobs may be, for example, cylindrical handles that one pulls or rotates to perform some function on the device, such as powering on or off the device, switching between modes of the device, or controlling a setting on a device, such as adjusting a volume, a brightness of a display, a temperature, a speed, or other control operations.
FIG. 1C illustrates a conventional clothes dryer 130 with a mechanical control knob 131 that controls at least a portion of the operations of the clothes dryer 130. An operator of the clothes dryer uses a complete hand to rotate the mechanical control knob 131, for example, to change the operational mode of the clothes dryer 130, adjust the temperature of the clothes dryer 130, or the like.
The conventional devices that implement mechanical control knobs are subject to wearing of the moving parts from regular use. In a conventional mechanical knob-controlled interface, the mechanical knob mounts to a shaft, with the shaft passing through a bushing to get through an opening of the front panel. The openings that allow mechanical motion of the mechanical knob subject the device to possible contamination, for example, from water, dirt, corrosives, or the like. In addition, these openings may allow paths for electrostatic discharge (ESD) events into the circuitry of the control panel. Another disadvantage of mechanical control knobs is that the top surface of the knob has a limited use due to the required motion of the mechanical control knob. Another disadvantage is that upon power loss, the mechanical control knob may leave the device in a dangerous condition when the power is restored.